The presently disclosed subject matter relates to a clutch plate and a method of producing the same.
There is a friction clutch which performs power transmission, by frictionally engaging a clutch plate at a driving side with a clutch plate at a driven side. Moreover, there is a friction clutch of electromagnetic type using a clutch plate which is provided with a plurality of windows in a shape of an arc-shaped through hole. The windows are required for forming a magnetic circuit. The friction clutch of the electromagnetic type is disclosed, for example, in JP-A-H11-303911.
Further, an electronically controlled 4WD coupling (ITCC (registered trade mark)) in which the electromagnetic friction clutch is used is disclosed, for example, in JP-A-2002-213485.
The clutch plate is provided with lubricating grooves for holding lubricating oil and for relieving the lubricating oil, on occasion of frictional engagement between the plates, on both end faces thereof in an axial direction. The lubricating grooves are extensively formed on sliding faces, and include a plurality of grooves. There are a plurality of intersection points where the grooves intersect with each other.
In forming the lubricating grooves, a method in which the lubricating grooves are formed with plastic deformation, in a same phase on both the end faces in the axial direction, is considered. According to this method, a flattening step can be omitted, because the lubricating grooves are formed in the same phase. Therefore, it is possible to produce the clutch plate by sequentially forwarding press work in which a groove pressing step, an extracting step, and so on are carried out in parallel at a time.
Specifically, the sequentially forwarding press work is to carry out a series of works which are performed through a provisional extracting step, a groove pressing step, and a shape extracting step on a sheet of magnetic metal plate M, in parallel at one press work, as shown in FIG. 8. According to the production method in which the sequentially forwarding press work is applied to production of the clutch plate, it becomes possible to reduce cost for the press work.
However, in case where the lubricating grooves are formed with the plastic deformation in the same phase on both the end faces in the axial direction, in the production process, bottom parts of the grooves are subjected to compression stress from both faces, and work-hardened. Those parts where the grooves are to be formed in edge parts of the clutch plate are likely to become fragile due to this work hardening. The stress is particularly concentrated on the intersection points where the grooves intersect with each other, and there is such anxiety that the edges of the clutch plate may be broken during the production. In case where the clutch plate is broken and a broken part remains in a stamping die, for example, there is such anxiety that a crack or a mark may occur at the next press work, and a life of the die may be deteriorated.